Preparation of alkyl bromides



3,000,980 PREPARATION OF ALKYL BROMIDES Arthur A. Asadorian, Midland,and George A. Burk, Bay City, Mich., assignors to The Dow ChemicalCompany, Midland, Mich., a corporation of Delaware N Drawing. Filed Apr.7, 1958, Ser. No. 726,607 7 Claims. (Cl. 260-658) The present inventionrelates to bromination of organic compounds and more particularlyrelates to the replacement of chlorine with bromine in chlorinatedaliphatic compounds. Further, the present invention relates to thesimultaneous bromination of both aromatic and aliphatic compounds andaliphatic chloro compounds.

It has been found that a saturated aliphatic halohydrocarbon containingat least one chlorine atom can be brominated with hydrogen bromide inthe presence of ferric chloride. Alternatively, it can be brominated byhydrogen bromide formed in situ by the bromination of a hydrocarboncompound, which may contain halogen substituents and having areplaceable hydrogen atom, with bromine in the presence of ferricchloride. Thus, it has now been found possible to brominate aromatic,haloaromatic, paraffinic or haloparaflinic compounds With bromine andferric chloride and simultaneously replace chlorine in a saturatedhalohydrocarbon with the bromine of the HBr generated in situ.

In one manner of carrying out the present invention a saturatedhalohydrocarbon containing at least one chlorine atom attached to analiphatic carbon atom is contacted with hydrogen bromide in the presenceof ferric chloride. The hydrogen bromide is employed in a molar amountat least equal to the chlorine atoms to be replaced. Thus, if a singlechlorine atom is to be replaced at least one mole of hydrogen bromide isemployed for each mole of chlorine containing reactant; if two chlorinesthen two, etc. The reaction proceeds smoothly when the reactants arecontacted at temperatures of from 25 to 120 C. The catalyst ispreferably employed in amounts of from 0.5 to percent by weight based onthe chlorine containing reactant.

Alternatively, the hydrogen bromide of reaction may be generated insitu. Thus, a hydrocarbon compound which may contain halogensubstituents and having a replaceable hydrogen atom may be brominatedwith bromine in the presence of felric chloride and in the presence of asaturated halohydrocarbon to produce the brominated hydrocarbon andhydrogen bromide in situ which will react with the saturatedhalohydrocarbon to replace chlorine therein, in the manner hereinbeforedescribed.

The reactions which occur may be characterized as follows:

(I) FeOla RC1+HBr RBr+HOl In either case the products of the reactioncan be conveniently separated by fractional distillation.

Substantially any organic compound can be employed in accordance withthe present invention as long as it is within the defined scope of thematerials, i.e., in the first instance, wherein hydrogen bromide is thereactant the compound is a saturated halohydrocarbon which contains atleast one chlorine atom attached to an aliphatic carbon atom and, in thesecond instance, any of the afore mentioned compounds or any aromatic,aliphatic haloaromatic or haloaliphatic compound which has a replaceablehydrogen atom.

Thus, one can employ as the saturated halohydrocarbon compound, carbontetrachloride, chloroform, dichloromethane, bromotrichloromethane,nichloroethane,

Patented Sept. 19, 1961 Ice propylene dichloride, ethylene dichloride,chlorobromethane l-chloro-propane, 2-chloro propane, and the like. Asthe replaceable hydrogen-containing hydrocarbon or halohydrocarboncompound one can employ benzene, toluene, naphthalene, chlorobenzene, o,m or pchloro-toluene, the propanes, the butanes, the pentanes, hexanes,heptanes and their home or chloro derivatives, and the like. Further,the chloro compound and the organic compound may be one and the same,for example, one'can employ pentachloroethane to obtaindibromotetrachloroethane. i

The use of the ferric chloride catalyst is considered essential since itdoes not catalyze condensation and isomerization reactions in the usualmanner expected of Friedel- Crafts type catalyst.

The following examples illustrate the present invention but are not tobe construed as limiting.

Example 1 5 moles of benzene dissolved in 5 moles of carbontetrachloride containing two percent by Weight of ferric chlo ride washeated to the reflux temperature (76 C.) and 620 grams (3.87 moles) ofbromine added in a portionwise manner over a six and one quarter hourperiod. During the addition, hydrogen chloride gas was evolved. Uponcompletion of the evolution of hydrogen chloride of reaction, the crudeoil was washed and neutralized. It weighed 1487 grams and bydistillation analyzed 35 percent bromobenzene, 5 percentparadibromobenzene, 20 percent CBrCl 20 percent CBr Cl the remainder CCIHalf of the bromine feed, or percent of the theoretical bromine, wasfixed in the aromatic and 92 percent of generated byproduct HBr wasconverted to alkyl bromides.

Example 2 In a like manner, employing toluene in place of benzene, 2.2percent by weight of ferric chloride and a temperature of 86 to 96 C.,there was obtained orthoand para-*bromotoluene andbromotrichloromethane.

Example 3 In like manner of Example 1, employing equal volumes of1,2-dibromopropane and CCL; containing 0.34 percent FeCl and atemperature of from 70-105" (3., there was obtained a mixture of 1,1,2-and 1,2,3-tribromopropanes mixed CBI'Clg, CBl'gClg, CBI'gC]. and CB1}.

Example 4 A mixture of 1000 cc. of carbon tetrachloride (1588 grams,10.3 moles) of 81 grams of FeCl (5 mole percent) Was treated with HBrgas by bubbling the gas into the reaction mixture over a 35 hour period.The reaction mixture was heated to from 40 to 70 C. over this period.The reactor was provided with a vent gas scrubher to recover theunreacted CCl There was obtained as a result of these operations 643 cc.(1382 grams) of product as an oil. This is a 79.5 percent yieldcalculated tor CBrCl Analysis of product was:

1. A process for preparing bromine-containing compounds which comprisescontacting an organic compound selected from the group consisting ofaromatic, halo-.

genated aromatic, paraflinic and halogenated paraifinic hydrocarbons andhaving a replaceable carbon bound H atom in the molecule, which compoundmay also contain halogen atoms, with bromine and a saturated aliphatichalohydrocarbon containing at least one chlorine atom in the presence offerric chloride.

2. A process as set forth in claim 1, wherein the organic compound is anaromatic compound.

3. A process as set forth in claim 1, wherein said organic compound isan alkane.

4. A process as set forth in claim 1, wherein said organic compound is ahaloalkane.

5. A process as set forth in claim 1, wherein the organic compound andthe saturated halohydrocarbon are the same.

6. A process for preparing bromine-containing saturated aliphatichalohydrocarbons which comprises contacting a saturated aliphatichalohydrocarbon containing at least one chlorine atom with hydrogenbromide and ferric chloride. 2

7. A process as set forth in claim 6 wherein the contacting is done at atemperature of from 25 to 120 C.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES Scheufelan: Liebigs Annalen der Ohemie, 23 1, 152-195 (1885),pp. 152155 and 186188 especially relied on.

1. A PROCESS FOR PREPARING BROMINE-CONTAINING COMPOUNDS WHICH COMPRISESCONTACTING AN ORGANIC COMPOUND SELECTED FROM THE GROUP CONSISTING OFAROMATIC, HALOGENATED AROMATIC, PARAFFINIC AND HALOGENATED PARAFFINICHYDROCARBONS AND HAVING A REPLACEABLE CARBON BOUND H ATOM IN THEMOLECULE, WHICH COMPOUND MAY ALSO CONTAIN HALOGEN ATOMS, WITH BROMINEAND A SATURATED ALIPHATIC HALOHYDROCARBON CONTAINING AT LEAST ONECHLORINE ATOM IN THE PRESENCE OF FERRIC CHLORIDE.